Cartesian Diver

A **Cartesian diver** is a small device, often made from a glass tube with a small amount of water inside, or even a simple dropper, that demonstrates the principle of buoyancy. When the diver is placed in an upright, tall, closed plastic bottle filled with water, it can be adjusted to achieve neutral buoyancy, allowing it to float on the water's surface. The diver's ability to rise or sink depends on its overall density. When the diver's overall density, including the glass tube and air, is less than that of water, it will float, and when its overall density becomes greater than that of water, it will sink. By squeezing the bottle, the pressure applied compresses the air inside the diver, reducing its volume. This compression increases the diver's density, and when it becomes greater than the density of the surrounding water, the diver sinks.